Method and apparatus for coating metal strip



Feb. 25, 1969 B. c. coAD 3,429,734

METHOD AND APPARATUS FOB COATING METAL STRIP Filed oct. 24, 1965 H613.-5/ FIGA.

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United States Patent Ofi 'ice 3,429,734 Patented Feb. 25, 1969 CiaimsABSTRACT OF THE DISCLOSURE A crucible for a melt of a metallic coatingmaterial is provided with a rectangular slot in its bottom. The slot isof substantially the same size and shape as the transverse cross sectionof a solid metal strip to be coated. The strip is continuously drawn upthrough the slot. The crucible up to a certain level contains a melt ofthe coating material through which the core material is drawn and leavesthe melt at said level. The strip being cooler than the melt absorbsheat therefrom to congeal it on the strip. Extending from the bottom ofthe crucible to points above said level and located at opposite ends ofthe slot are members grooved to slidably tit with the margins of thecore material so as to act as shields against the melt reaching marginalportions of the strip, whereby the effect of the uneven marginalheat-How pattern is avoided and a constant thickness of coating congealson the strip between its uncoated margins. The uncoated margins maylater be trimmed off.

This invention relates to the manufacture of coated materials, and moreparticularly to the application to a core `by a dip-coating process of acoating of substantially constant thickness.

Among the several objects of the invention may be noted the provision ofa method and apparatus for applying a coating of substantially constantthickness to a core by dip-coating the core in a melt of the coatingmetal; the provision of a method and apparatus of the class describedfor coating a metal core with a like or different metal coating ofsubstantially uniform thickness; the provision of a method and apparatusfor the manufacture of a coated core by a continuous process wherein thecoating is excluded from certain portions of the core; and the provisionof an article coated in accordance with the method of the invention.Other objects and features will be in part apparent and in part pointedout hereinafter.

The invention accordingly comprises the methods, constructions andproducts hereinafter described, the scope of the invention beingindicated in the following claims.

In the accompanying diagrammatic drawings, in which one of variouspossible embodiments of the invention is illustrated:

FIG. 1 is an illustrative cross section through a coated stripmanufactured by a prior-art process;

FIG. 2 is a similar section through a coated strip manufacturedlaccording to the present invention;

FIG. 3 is a top plan view of apparatus useful for manufacturing coatedstrip according to the invention;

FIG. 4 is a bottom plan view of the FIG. 3 apparatus;

FIG. 5 is a fragmentary perspective view of parts of the apparatus; and

FIGS. 6 and 7 are enlarged fragmentary sections taken along lines 6-6and 7 7, respectively, of FIG. 3.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

In the present application, reference yto metals is intended to includealloys thereof. Coating of elongate core material may be with a materialwhich may be the same as or different from that of the core. For clarityof illustration, the sizes, thicknesses, etc. are exaggerated. Thereforethe drawings are not to scale. The term core means that which is coatedor clad and may be in the form of strip, rod, wire or any otherappropriate cross section. The invention has primary, although notexclusive, use when both the core and the cladding are composed ofdfferent metals.

It is known in the art to form clad metal wire, rod, strip or the likeby drawing a cold core through molten metal to congeal or freeze a lm orlayer of the melt on `the core. The thickness of the congealed metaldepends (in part) on the heat-flow pattern developed in the solid core.This heat-flow pattern, and thus the layer coated on the core, areasymmetrical across a core which has an unsymmetrical heat-flow pattern;for example, a strip which is rectangular in transverse section.

In FIG. l of the drawings is shown a metal core strip 1 of rectangularcross section, coated with metal 3 which has been congealed on the coreby drawing it through a melt of the coating metal in accordance with aprocess previously known to the art. As shown in FIG. l, the surface ofthe coating metal is somewhat oval in section, a shape which isundesirable in that the cladding on the wide faces of the strip is ofvariable thickness. Thus even if the edges are trimmed off, as on thedotted lines 2, an uneven coating occurs on the flat sides of the strip.This asymmetrical coating results from an uneven heat-iiow pattern atthe corners of the core, and it is avoided by the present invention.

Referring now to FIGS. 3-7 of the drawings, apparatus for manufacturinga metal strip having on it a congealed coating `of substantially uniformthickness Iis `shown to comprise a refractory container or Crucible 5having a bottom or base 7 and a wall 9 projecting upward from the base.Crucible `S is adapted to receive a melt of the coating metal. In thebase 7 of the Crucible is a hole 11 which is substantially the `same`size and shape as the transverse cross section of the core to becoated. As illustrated in the drawings, the hole 11 is in the shape of arectangle but it will be understood that other shapes can he used. Thecore or so-called seed strip to be coated is designated 13 and, as shownin the drawings, is an elongated strip which is rectangular in crosssection. Crucible 5 is open at the top as illustrated in FIG. 4 so thatstrip 13 may be drawn upward through hole 11 and through the melt l5 ofthe coating metal (FIGS. 6 and 7) and then out through the top of thecrucible. The core is cooler than the melt when it first enters thecrucible. If desired, this temperature differential can be establishedand regulated by contr-olling the temperature `of the strip as it entersthe melt.

A pair of refractory guides or shields 17 are secured to base 7 atopposite ends -of the slot 11. Each `of guides 17 has a notch or guideslot 19 on its inner or facing surfaces, the innermost portions of theslots being spaced apart a distance just adequate to receive the sideedges of the core 13 as it is drawn upward through hole 11. Guides 17not only guide the core upward but also serve to shield or mask the edgeportions of the core from the melt 15 as the core is drawn through themelt. The guides 17 extend from the base 7 upward to a point yabove theupper level of the melt in the crucible. Thus there is substantially nocontact between edge portions of the core and the melt as the core ismoved through the guides.

As the core 13 moves upward through the crucible, as indicated by thearrows in FIG. 5, the relatively hot liquid metal 15 in the cruciblewill engage the Unshielded center portions `of core 13 (i.e., theportions between the guides 1-7). This material will be cooled bycontact with the cooler surface of the core and will congeal on theunshielded core surface. The coating strips which have been designated21, increase in thickness as the core moves from the bottom to the topof the melt, and this buildup is illustrated in FIG. 7 of the drawings.The thickness of strips 21 will depend upon the mass of core 13, thespeed at which it is moved through melt 15, and the temperaturediiferential between the core and the melt.

In order to obtain a coating of constant thickness, an even heat-flowpattern must be developed across -all surfaces to be coated. The onlyareas of core 16 exposed to the melt are the hat central surfaces on itsopposite sides. The heat transfer along these surfaces is substantiallyeven 4or regular, there being no irregular configuration as at theshielded corners, or variance in thickness of Ithe strip which wouldtend to develop an irregular heat-flow pattern along these areas. Theend portions of the core or strip 13 which are shielded by the guides 17contain the corners or edges `of the strip across which irregularheat-flow patterns are developed. Were these edge surfaces exposed tothe melt, an irregular coating thickness would occur on the at sidesurfaces, similar in shape to the coating 3 illustrated in lFIG. 1,since an uneven heat-flow pattern would be developed. Thus by shieldingthe areas of the core being coated which might develop irregularheat-dow patterns, constant thickness of coatings can be applied to thefiat surfaces of the core.

A transverse cross lsection of the coated strip is illustrated in FIG. 2of the drawings. It will be noted that coatings 21 on each side of core13 are substantially the same thickness and are constant in theirthickness throughout a substantial width. If desired, the uncoated endsof core 1'3 may be trimmed off. The resulting article thus produceddiers significantly from the coated strip of the prior art illustratedin FIG. l which has a coating of variable thicknesses on its flat sides.The article illustrated in FIG. 2 is useful in many applicationsrequiring clad strips or the like.

The process of the invention has been described in connection withcoating of a thin metal strip of rectangular cross section. However, itis to be understood that cores of other shapes or configurations mayalso be coated according to -this process. It will also be recognizedthat coating material can be excluded from areas of the core other thanedges `or other areas which might produce uneven coatings. For example,narrow strips might be applied to opposite sides of a circular core inwhich the heat-flow pattern is even. Other variations will be clear tothose skilled in the art.

It will be understood that while the materials of the core and of thecongealable cladding material are in general different, these materialsmay be the same if the object of the method is simply to increase thethickness of the strip by dip-forming. In the preferred form, bothmaterials are metal, but other materials may be employed.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

What is claimed is:

1. The method of continuously evenly applying and congealing meltedmetal coating material on at least one face of an elongate solid metalstrip having a crosssectional shape providing at least one face areaover which an even heat-How pattern may be developed and marginal areasat which irregular heat-flow patterns ordinarily develop to distort saideven heat-ow pattern, comprising sliding the strip through groovedguides for shielding the margins of the strip while leaving unshieldedat least one face of the strip, and immersing the strip in a melt of themetal coating material only in the region of its movement through saidguides, whereby the melted metal congeals substantially evenly on saidface.

2. The method according to claim 1, wherein both faces of the strip areleft unshielded during immersion.

3. Apparatus for continuously evenly coating a metal on at least oneface of an elongate solid metal strip having a cross-sectional shape ofsubstantially constant thickness providing opposite face areas overwhich even heatow patterns may be developed except for marginal areas atwhich irregular heat-ow patterns ordinarily develop to distort said evenheat-dow patterns, the apparatus comprising a crucible adapted to hold amelt of the coating metal up to a certain level, the crucible having aslot in its space conforming generally to the transve-rse cross sectionof the strip to be coated, means for moving the strip upwardly throughthe slot and through the melt to absorb heat therefrom to congeal on thestrip, and grooved means in the crucible extending from the 'base of thecrucible adjacent the ends of the slot to points above said level of themelt for slidably receiving and shielding said marginal areas of thestrip from the melt during passage of the strip therethrough, wherebydevelopment of said irregular heat-ow patterns is substantiallyprevented from occurring and said even heat-flow patterns aresubstantially maintained.

4. Apparatus made according to claim 3, wherein the strip and the slotin the base of the crucible are of rectangular cross section.

References Cited UNITED STATES PATENTS 3,320,084- 5/1967 Lirones 117-38X 3,134,150 5/1964 Parke et al. 118-405 3,060,055 10/ 1962 Bixler118-405 1,711,948 5/1929 Jones 118-406 ALFRED L. LEAVITT, PrimaryExaminer.

A. GRIMALDI, Assistant Examiner.

U.S. Cl. X.R. 118-405; 117-114

